Old English fleot "a ship, raft, floating vessel," also, collectively, "means of sea travel; boats generally," from fleotan "to float" (see fleet (v.)). Sense of "naval force, group of ships under one command" is in late Old English. The more usual Old English word was flota "a ship," also "a fleet; a sailor." The fleet for "the navy" is from 1712.

The Old English word also meant "estuary, inlet, flow of water," especially the one into the Thames near Ludgate Hill, which lent its name to Fleet Street (home of newspaper and magazine houses, standing for "the English press" since 1882), Fleet prison (long used for debtors), etc.

"swift," 1520s, but probably older than the record; apparently from or cognate with Old Norse fliotr "swift," from Proto-Germanic *fleuta, which is related to the source of fleet (v.). Related: Fleetness.